#include <stdio.h>
double cacl(double a, double b);
int main(void)
{
    double a, b;

    printf("输入两个浮点数：");
    scanf("%lf %lf", &a, &b);
    while ( a > 0 && b > 0)
    {
        printf("答案是：%lf\n", cacl(a, b));
        printf("输入两个浮点数：");
        scanf("%lf %lf", &a, &b);
    } 
    printf("程序结束！\n");

    return 0;
}

double cacl(double a, double b)
{
    return (a - b) / (a * b);
}
